Physiological Traits Associated with Tolerance to Stagnant Flooding in Rice

High rainfall usually causes flooding, adversely affecting rice production in developing countries. Recently, varieties have been developed that overcome losses caused by complete submergence by introgression of the SUB1 gene into popular varieties. However, Sub1 varieties do not perform well under long-term partial stagnant flooding (SF; 20-50 cm) that predominates in large areas of rainfed lowlands. A set of selected genotypes, including two Sub1 varieties were subjected to SF with water depth increased by 10 cm weekly after transplanting until it reaches 55 cm, then maintained through maturity. Water depth in the control plots was kept at 5 cm. The study aims to understand the bases for variation in SF tolerance observed among selected rice genotypes. IRRI 119 and IRRI 154 had higher survival and yield than PSBRc18-Sub1 and Swarna-Sub1 under SF. Swarna-Sub1 did not survive, whereas PSBRc-Sub1 performed poorly with low survival and low yield. Stagnant flooding increased shoot elongation but decreased tiller number and dry matter accumulation. The contribution to shoot elongation by the leaf sheath was 59% while that of the leaf blade was 41%. Concentrations of soluble sugars in leaves and roots decreased but those in the stem increased. Correlations of length of leaf blade at day 7 of treatment with survival at maturity (r = 0.77**) and with yield (r = 0.86**) were high. Stem dry weight per plant measured 7 d after imposition of SF correlated significantly with survival (r = 0.70**) and with yield (r =0.54**). Root soluble sugar concentration had highest correlation with survival (r = 0.60** ) and with yield (r = 0.60**) at day 28 of the treatment. These traits could be further verified and used to identify quantitative trait loci associated with tolerance to SF for breeding new cultivars tolerant to prolonged partial SF.

强降雨通常会引发洪涝灾害，对发展中国家的水稻生产造成不利影响。近年来，科研人员通过将SUB1基因（SUB1 gene）渗入主流水稻品种中，培育出了能够抵御完全淹涝导致的产量损失的水稻品种。然而，SUB1品种在长期局部滞涝（SF；水深20~50 cm）环境下表现不佳，而这类滞涝场景在雨养低地的大片区域中广泛存在。本研究选取了一组基因型材料（包含两个SUB1品种），对其施加滞涝处理：移栽后每周将水深提升10 cm，直至达到55 cm后维持该水位至水稻成熟，对照小区的水深则始终维持在5 cm。本研究旨在阐明所选水稻基因型间滞涝耐受性差异的成因。实验结果显示，在滞涝处理下，IRRI 119与IRRI 154的存活率及产量均高于PSBRc18-Sub1和Swarna-Sub1；其中Swarna-Sub1未能存活，而PSBRc-Sub1表现极差，存活率与产量均较低。滞涝环境会促进水稻株高伸长，但会降低分蘖数与干物质积累量。叶鞘对株高伸长的贡献率为59%，叶片则为41%。叶片与根系中的可溶性糖浓度有所下降，而茎秆中的可溶性糖浓度则有所上升。相关性分析结果表明，处理第7天时的叶片长度与成熟期存活率（相关系数r=0.77**）及产量（r=0.86**）均呈显著正相关；施加滞涝处理7天后测得的单株茎秆干重与存活率（r=0.70**）及产量（r=0.54**）均呈显著相关；在处理第28天时，根系可溶性糖浓度与存活率（r=0.60**）及产量（r=0.60**）的相关性最高。上述性状可进一步验证，并用于筛选与滞涝耐受性相关的数量性状位点（quantitative trait loci），从而培育出适应长期局部滞涝环境的水稻新品种。